Some common insect pests of agronomically important crop plants such as tomatoes include the South American Tomato Leaf Miner (Tuta absoluta), stink bugs, cutworms, hornworms, aphids, cabbage loopers, whiteflies (Bemisia and Trialeurodes), fruitworms, flea beetles, spider mites such as Tetranychus urticae (the glass house red spider mite), Panonychus ulmi (fruit tree red spider mite) and Panonychus citri (citrus red mite), insects of the order Diptera, and Colorado potato beetles (Leptinotarsa decemlineata).
For example, whiteflies of the genera Bemisia (sweet potato whitefly) and Trialeurodes (greenhouse whitefly) are major pests of crop plants throughout the world, causing economic losses especially due to the transmission of plant viruses during feeding (i.e. they act as ‘virus vectors’). Bemisia tabaci is capable of transmitting more than 60 different members of the Geminiviridae, many of which belong to the Begomoviruses such as African cassava mosaic virus (ACMV), Bean golden mosaic virus (BGMV), Bean dwarf mosaic virus, Tomato yellow leaf curl virus (TYLCV), Tomato mottle virus (ToMoV), and others, plus a number of criniviruses. Both tropical and temperate crops are affected, such as tomatoes, beans, cucurbits, potatoes, cotton, cassava and sweet potatoes.
To date, the main control strategy for insect pests is the application of insecticides, aimed at killing adults, juveniles and eggs. Besides the substantial costs of insecticide application this practice has a severe environmental impact. Moreover, many insect pests are difficult to control with insecticides due to emerging resistance to the active ingredients.
In order to reduce insecticide application, there is a need for new ways of controlling crop damage and losses due to plant insect pests, both in field-grown and greenhouse-grown crops. From literature it is known that volatile components can directly influence insect behaviour (e.g. Bruce et al., 2005, Trends Plant Sci. 10: 269-74). One way to control virus transmission by plant insect pests is by identifying insect repellents, which can be applied on or near the crop plants or can be produced in the crop.
EP 0 583 774 describes the use of vegetable oil to reduce phytotoxicity of foliar insect control agents, whereby any type of insect control agent may be used.
Glandular trichomes are prominent on foliage and stems of the genus Lycopersicon (now classified as Solanum) and have been shown to produce a large number of secondary compounds, such as mono- and sesquiterpene hydrocarbons, sesquiterpene acids, methylketones and sugar esters. Several studies have tried to correlate the density of glandular trichomes with resistance against plant pests, such as maize earworm (Heliothis zea) or Colorado potato beetle (Kauffman and Kennedy, 1989, J Chem Ecol 15, 1919-1930; Antonious, 2001, J Environ Sci Health B 36, 835-848 and Antonious et al. 2005, J Environ Sci Health B 40: 619-631). Also the methylketones 2-undecanone and 2-tridecanone, stored in the glandular trichomes of L. hirsutum f. glabratum (renamed to S. habrochaites) were shown to exhibit a toxic effect against fourth instar larvae of Colorado potato beetle and adult whiteflies B. tabaci, respectively (Antonious et al. 2005, J Environ Sci Health B 40: 619-631).
Antonious and Kochhar (J Environm Science and Health B, 2003, B38: 489-500) extracted and quantified zingiberene and curcumene from wild tomato accessions with the goal of selecting wild tomato accessions that can be used for the production of sesquiterpene hydrocarbons for natural insecticide production. However, whether such compounds are able to be used as whitefly repellents or attractants was not disclosed. It is mentioned that zingiberene has been associated with Colorado beetle resistance and beet armyworm resistance, while curcumene has been associated with insecticidal effects. The wild tomato species L. hirsutum f. typicum (S. habrochaites) is mentioned to be resistant to B. argentifolii (now named B. tabaci) (Heinz et al. 1995, 88:1494-1502), but trichome based plant resistance could, of course, have various causes and from this paper one cannot make inferences regarding the presence or identity of compounds which have properties for attracting or repelling whiteflies.
Freitas et al. (Euphytica 2002, 127: 275-287) studied the genetic inheritance of the genes for the production of both the sesquiterpene zingiberene and glandular trichome types I, IV, VI and VII in interspecific crosses between L. esculentum (S. lycopersicum; cultivated tomato, no zingiberene) and wild L. hirsutum var. hirsutum (S. habrochaites; high in zingiberene). Zingiberene content in F2 plants contributed to B. argentifolii (B. tabaci) resistance by correlation and it was suggested to breed plants with simultaneously high levels of zingiberene, 2-tridecanone and/or acylsugars to contribute to higher levels of whitefly resistance.
ES 2341085 discloses exogenous application of alpha-zingiberene as a repellent and insecticide against T. absoluta and other insects that affect tomato crops. Alpha-zingiberene may be applied in its pure form, or in its natural form through the use of essential oils containing the molecule in appropriate concentrations.
De Azavedo et al., Euphytica 2003, 134, 247-351 describe the effect of endogenous zingiberene mediated resistance to T. absoluta. 
According to Pushkar, N. K. and Balawant, S. J. (2001) “Alternative medicine: Herbal drugs and their critical appraisal” in Jucker, E. Progress in Drug Research, Vol. 57, ginger essential oil contains alpha-zingiberene, but not 7-epizingiberene (Table 4, page 46).
Bleeker et al., Phytochemistry 2011, 72(1):68-73 disclose that 7-epizingiberene and R-curcumene, both purified from Solanum habrochaites (PI127826), act as repellent to Bemisia tabaci whiteflies, while stereoisomers alpha-zingiberene and S-curcumene from Zingiber officinalis oil (ginger oil) do not. Bio-assays showed that a cultivated tomato could be made less attractive to B. tabaci than its neighbouring siblings by the addition of the tomato stereoisomer 7-epizingiberene or its derivative R-curcumene (abstract).
Davidovich-Rikanati et al., The Plant Journal 2008, 56(2):228-238 disclose the transformation of tomato plants with a construct harbouring the alpha-zingiberene synthase of lemon basil (Ocimum basilicum L.) coupled to the fruit ripening-specific tomato polygalacturonase promoter (PG). The overexpression of alpha-zingiberene synthase results in the production of alpha-zingiberene by the transgenic tomatoes. It is further described that alpha-zingiberene is a major leaf oil sesquiterpene in Solanum hirsutum, and this trait has been associated with resistance to B. tabaci. 
Iijima et al., Plant Physiology 2004, 136(3):3724-3736 disclose the isolation and expression in E. coli of an alpha-zingiberene synthase of sweet basil.
Although several methods exist for combating plant insect pests, there is still a need for adequate protection against insect pests such as, for example, B. tabaci. 